The present invention relates to lockable differential gears for motor vehicles with a transmission or gear housing and a differential housing rotatably supported therein as well as with a lamellae set arranged in the differential housing which is adapted to be acted upon from the outside with a locking force.
Such a differential gear is disclosed in the DE-OS No. 33 13 283. In one construction of this prior art publication, a hydraulic piston displaceably arranged in the gear housing is rotatably supported by way of a radial bearing on a wheel output shaft. The axle shaft gear is seated at the other end of the wheel output shaft protruding into the differential housing, secured by way of a thrust ring. The lamellae set representing the differential locking means is provided, in turn, between the axle shaft gear and the differential housing. Upon actuation of the locking mechanism, the piston seeks to pull the output shaft toward the outside which thereby takes along the axle shaft gear by way of the thrust ring. The axle shaft gear presses the lamellae set against a support wall of the differential housing and effects a friction-locking connection between the differential housing and the wheel output shaft.
A disadvantage of this prior art solution resides in that the force path during actuation of the differential locking mechanism leads by way of the radial bearing arranged between the hydraulic piston and the wheel output shaft. The radial bearing must be dimensioned correspondingly large in order to withstand the loads. However, this is not always desirable not only for cost reasons, but also for space reasons. A further and much greater disadvantage exists with this prior art construction in that as a result of the transmitted torque the tooth pressure which exists between the differential bevel gear and the axle shaft gear, seeks to displace the axle shaft gear in the direction toward the lamellae set and therewith to lock the differential gear up to a certain degree. In other words, during normal driving operation, the prior art differential locking mechanism always exhibits a certain and undesired locking action.
In a further embodiment of the aforementioned prior art publication, a lamellae carrier is provided between the lamellae set and the wheel output shaft, which is non-rotatably seated on this shaft by way of a spline-tooth arrangement, but is axially displaceable on the shaft. The axle shaft gear is held on the lamellae carrier by way of a further spline-tooth arrangement which axle shaft gear is again supported at the differential housing. It is achieved in this manner that the previously described disadvantage of a continuing locking of the differential gear as a result of the tooth pressure does not occur. However, this solution entails a different disadvantage. The moment introduced by way of the drive pinion and the differential bevel gears is conducted from the axle shaft gear by way of the lamellae carrier to the output shaft and the individual teeth of the spline-tooth arrangement are pressed against one another. If the differential locking mechanism is engaged in this operating condition and if the locking action is again to be cancelled, the lamellae carrier can no longer be axially moved owing to this jamming action in the spline-tooth arrangement. The gear remains locked until the driving torque is taken back.
In a further embodiment, the lamellae set is again supported at the axle shaft gear whereby the latter further conducts the abutment force of the lamellae into the differential housing by way of the teeth of the differential bevel gears. The disadvantage of this solution resides in that during the locking the differential housing together with its spur bevel gear is axially displaced slightly by reason of the force path. However, the spur bevel gear meshes with the drive pinion with a very accurately adjusted tooth play. During the locking operation, this tooth play is therefore changed which may lead to jamming, distortions, and noise developments.
It is the object of the present invention to so further develop a differential gear of the aforementioned type that the aforementioned disadvantages do not occur, in which excessively large roller bearings are not needed, especially for the transmission of the locking forces, in which a safe disengagement is assured after the locking, in which the locking action occurs only with an intentional pressure admission and finally in which the tooth play between spur bevel gear and drive pinion is not impaired during a locking operation.
The underlying problems are solved according to the present invention in that the acted-upon lamellae set is supported at the gear of transmission housing by way of an axial bearing.
The locking force is therefore supported according to this invention against the gear or transmission housing by way of an axial bearing. Such an axial bearing permits a considerably higher load capacity than the radial bearings mentioned in the prior art so that the bearing does not assume any unacceptable dimensions.
In an appropriate construction according to the present invention, a transmission member is provided between the lamellae set and the axial bearing. This transmission member is separate from the differential housing from a force point of view and can thus transmit the locking force to the transmission housing without influence on the differential housing. In a preferred embodiment, the transmission member includes a circular ring which is slipped over an external guidance of the differential housing. The circular ring abuts with one end face at the axial bearing arranged at the transmission housing. The opposite side thereof passes over into fork-shaped arms which engage into the differential housing and cooperate with the lamellae set.
In another preferred embodiment, the axial bearing is located between a wheel output shaft and the gear or transmission housing. A thrust ring is provided for this purpose between the lamellae set and the wheel output shaft which introduces the locking force into the wheel output shaft. The thrust ring may thereby be provided ahead of the axle shaft gear so that the force path leads by way of the axle shaft gear. However, it should be noted with this solution that the distance between the thrust ring and the bearing seat of the axial bearing must be maintained very accurately in order to obtain the correct tooth play between axle shaft gear and differential bevel gears.
In a further advantageous embodiment of the present invention, the thrust ring is located to the rear of the axle shaft gear. A lamellae carrier is preferably provided in this case which acts on the thrust ring. The axle shaft gear remains free of loads in this construction during a locking operation. The advantage of this solution lies in the greater tolerance range between thrust ring and bearing seat of the axial bearing.
A further appropriate embodiment of the present invention is characterized in that the axial bearing is located between the differential housing and the transmission housing. In this construction, the lamellae set acts on an abutment shoulder of the differential housing which further transmits the loads onto the axial bearing.